red
from a severe crush. The ultimate result has been satisfactory, as one
or other end has always healed in normal position, and the function of
the arm has thus been maintained.

DISLOCATION OF THE SHOULDER

The shoulder is more frequently dislocated than all the other joints
in the body taken together. This is explained by its exposed position,
the wide range of movement of which it is capable, the length of the
lever afforded by the humerus, and the anatomical construction of the
joint--the large, round humeral head imperfectly fitting the small and
shallow glenoid cavity, and the ligaments being comparatively lax and
thin. The capsule of the joint is materially strengthened in its upper
and back parts by the tendons of the supra- and infra-spinatus and
teres minor muscles; while it is weakest below and in front, between
the subscapularis and teres major tendons. It is here that it most
frequently gives way and allows of the escape of the head of the bone.
The determining factor is probably that when the arm is abducted the
neck of the humerus comes in contact with the tip of the acromion, and
further abduction forces the head against the lower, weak portion of
the capsule, which gives way.

The violence is usually transmitted from the hand or elbow, less
frequently from the lateral aspect of the shoulder, the limb being
usually abducted and the muscles relaxed and taken unawares. The head
of the humerus, thus brought to bear on the weakest part of the
capsule, ruptures it and passes out through the rent. Dislocation is
readily produced in an unconscious person--as, for example, in
conducting artificial respiration in a patient suffering from opium
poisoning, the arms being hyper-abducted to exert traction on the
chest.

_Varieties._--Several varieties of dislocation are recognised,
according to the position in which the head of the humerus finally
rests (Fig. 17). The simplest of these is the _sub-glenoid_ variety,
in which the head rests on the long tendon of the triceps, where it
arises from the axillary border of the scapula just below the glenoid
cavity. In almost all dislocations of the shoulder the head of the
bone is at least momentarily in this position, but the sharp edge of
the scapula and the rounded head are ill adapted to one another, and
the position is not long maintained. The subsequent course taken by
the humerus depends upon the nature and direction of the force, the
position of the limb a